Conventionally, when a film is wound into a roll, the surface thereof is treated partially in the transverse direction of the film so as to prevent side slip and snake-like movement of the film. Examples of such surface treatments are embossing, formation of protruding stripe patterns, and electrification. Through these surface treatments, the friction coefficient between film layers can be increased and the adhesion between film layers can be improved, thereby preventing slip and snake-like movement of the film.
Among these surface treatments, an electrification process is disclosed in Japanese Unexamined Patent Application Publication No. 9-202496, for example. Japanese Unexamined Patent Application Publication No. 9-202496 discloses an electrification process for electrifying both surfaces of a film, comprising putting a discharge electrode close to or in contact with one surface of the film while having the other surface in close contact with a portion of a grounded conductive roller so as to charge the film, and then separating the film from the surface of the grounded conductive roller
However, in the invention described in Japanese Unexamined Patent Application Publication No. 9-202496, air trapped between film layers while the film is wound into a roll cannot escape through the film edges because the charged portions adhere to each other to prevent slipping during winding, resulting in wrinkles and decentering during rotation.
Especially in a vacuum process such as metallization of a film roll, air trapped between the film layers escapes at once during evacuation process in the vacuum apparatus, resulting in significant slips of the edges and snake-like movement of the film swinging to the left and right while the film is being unwound. Accordingly, a method of electrification of a film roll for metallization in a high vacuum in which high adhesiveness is achieved and air trapped between the film roll layers can adequately escape during winding has been desired.
Japanese Unexamined Patent Application Publication No. 51-71351 discloses a method for securing escapeways for air through edges of the film roll, employing a technology of intermittently imparting surface treatment, such as electrification or hot air, in the longitudinal direction of the film, the surface treatment being synchronized with the rotation of the film roll.
The technology disclosed in Japanese Unexamined Patent Application Publication No. 51-71351 is shown in FIG. 4. As shown in FIG. 4, when a film 4 is wound into a film roll 1, the film 4 is intermittently charged with a needle electrode 7 connected to a high voltage power supply 9. Moreover, the speed of rotation of the film roll 1 is detected with a rotation-speed detector 15 for the film roll 1 so as to control on/off of the high voltage output to synchronize with the rotation of the roll using a controller 12.
In this method, however, because the surface treatment by electrification is synchronous with the rotation of the winding roll, a complex and expensive controller 12 is required. Moreover, especially since the application cycle of the high voltage is varied in response to an increase in the rolled diameter of the film roll, switching of a high-voltage circuit is required. Since this system is complex, there is a problem in that the high-voltage switching section is vulnerable to damage.
Furthermore, because a voltage is intermittently applied to the needle electrode 7, adhesion and solidification of dust on the needle electrode and oxidation of the needle tip are significant, requiring extensive maintenance. Also, the needle tip changes shape due to corrosion, resulting in variation in discharge state over time and, eventually, in control failure.
Since each film layer adheres to the next at a particular position in the perimeter direction of the film roll, a difference in air distribution is generated in the perimeter direction when the rolled diameter is large, resulting in degraded roll quality. To be more specific, as shown in FIG. 4, a difference in the film roll hardness between a film adhesive portion 16 and a nonadhesive portion 17 is generated, resulting in a polygonal roll which causes tensile variation, film breakages, and wrinkles.
In the above known electrification process, the electrification process is performed in uneven manner, and when the film is wound into a film roll, the electrified portions are sequentially stacked at the same position of the film roll. Thus, the electric potential of this position significantly increases, and, as shown in FIG. 8, a discharge 22 occurs from the electrified portion to the neighboring nonelectrified portion, resulting in changes in the width of the electrified portion.
In view of the above, the known surface technology is not sufficient for preventing slipping of the film roll during winding.